Sphingosine-1-phosphate (S1P) is a biologically active sphingolipid that mediates vascular maturation. S1P is produced by platelets and mast cells and is released into the circulation where it is carried on high-density lipoproteins. S1P binds to 5 S1 P/Edg (endothelial differentiation gene) receptors on endothelial cells, smooth muscle cells and monocytes to mediate vascular effects, including cell survival, proliferation, and migration. This grant examines the role of S1P in preventing early events contributing to atherosclerosis and other vascular complications of Type 1 diabetes. Incidence of vascular complications and atherosclerosis is accelerated in Type 1 diabetes. Early initiating events of vascular complications and atherogenesis include endothelial activation and monocyte recruitment to vascular endothelium. The hypothesis of this application is that S1P prevents endothelial activation, thereby preventing vascular complications and onset of atherosclerosis in Type 1 diabetes. The grant is focused on identifying the mechanisms though which S1P prevents endothelial activation using the NOD/LtJ mouse, a model of Type 1 diabetes. Aim 1 will identify the specific mechanisms by which S1P prevents monocyte:endothelial interactions in NOD/LtJ mice. This will include identification of the specific Edg receptor signaling pathway that mediates the anti-inflammatory action of S1P in endothelium. A combination of ex vivo and in vitro appraoches using primary endothelial cells and monocytes from NOD/LtJ mice will be utilized to accomplish this Aim. Aim 2 will test the hypothesis that S1P regulates monocyte trafficking to aorta and kidney of Type 1 diabetic mice, thus reducing initiation of vascular complications of diabetes. GFP-labeled monocytes will be injected into S1Ptreated NOD/LtJ mice to track newly localized monocytes to aorta and kidney. Aim 3 will test the hypothesis that S1P prevents atherosclerosis through a reduction in monocyte/macrophage accumulation in aorta. This aim will utilize apoE-deficient mice that have been made diabetic through the use of streptozotocin (STZ). The apoE/STZ mouse is a recognized model of Type 1 diabetes that develops complex atherosclerotic plaques similar in composition to those found in humans. Identification of a novel anti-inflammatory signaling pathway in endothelial cells may lead to future therapeutic benefit for vascular complications of Type 1 diabetes.